High-frequency electromagnetic wave transmission system



S. RAMO July 6, 1954 HIGH-FREQUENCY ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM 3 Sheets-Sheet 1 Filed Aug. 13, 1942 Nouvnuaun JNVZSWOJ NOLLV/INELLLV w m Cl m m Wm .nm .6

S. RAMO July 6, 1954 HIGH-FREQUENCY ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM 5 Sheets-Sheet 2 Filed Aug. 15, 1942 Inventor: Simon iazmo, rd His Attorney S. RAMO July 6, 1954 HIGH-FREQUENCY ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM 3 Sheets-Sheet 3 Filed Aug. 15, 1942 Fig.7

OUTPUT AMPLIFIER ULTRA HIGH FREQUENCY GENERATOR 0R ANTENNA AMPLIFIER SIGNAL SOURCE OUTPUT INPUT ULTRA HIGH FREQUENCY Inventor: Sim on -Ram 0,

y H i A'btOTn ey Patented July 6, 1954 HiG'H-FREQUENCY ELECTROMAGNEEIC WAVE TRANSMKSS'ION SYS' EEM Simon Ran a, vSchenectady, Y., assignor to Genera E ect c mpa y, a o roraiion .Q

New'York Application August 13, 1942, Serial No. 454,710

' 3. Cla ms- My invention relates to systems for the transmission of ultra highjrequency electromagnetic :waves and to devices, for controlling the energy transmitted through dielectric wave guides. i i somewhat ene el yanpr ciated th high. irequency (electromagnetic waves :may he transmitted through dielectric guides when the frequency at which the guide is excited is greater than a critical minimum or cut-ofi frequency. Ihe energy is.,,transmitt ed through the dielectric o e-medi m with n-the uide The types of waves which may be transmitted dielectrically through guides of this nature are manifold and have heretofore been classified generally into-the and .H types in the ,E ty wavesih elect oma netic-W .ha eb thlon iitud na and t an ver compo e t o e e t c fie dbutenly tra s er component o neti field... By use o th Word trans e f i meant t ansverse .to thedi teqti npf .wave prqna- ,gat onthr ughth guide. jl t it uewav s, .the electroma n t waves. have bei lonsitudinal and transvers compo ent of ma net es eld .bll on y.at ens erseeomponentof ele triefie st .T e

' waves ,w i hme betra sm t e .thr u hsuifle of t s at .hevele eniiienti ed@ he th .s11l serints.v as indicated, :Em ndH m- T .subscrint ind ate .t e. Order and t e -.s bs eris .m indieat sthe mo of prop sa ion. Th orde -Q'fth .W veisd te mined by theman i rinwhich thefie din en ity varies,circumferentialiy ar und th axis, of the guidanwher a the models determineritbvth manner of its va et pn w th d t frqmtheexis o th eu de- Althoug hereinafter'in the discussion of my invention an @1 1 type of wave :is referred to, it is to be appreciated that gnyinvention is applicable with equal facility to other H type waves as well as to E- type waves. A

It is an object of my invention to provide new and p v d high re uen el c romagn i v-.vv av..e. transmiss ns m ,It, .is .another object -,of my inv ntion ;to provide new and improved systems for controlling thetransmission of electromagnetic waves dielectrically.

It is another object of .my-invention-to provide new and improved devices for controlling the energy transmittedthrough dielectric wave guides.

Itis-a further object. of um-y inventionto pro- ,videin. new and improved dielectric wave guide syst le ric i cha dev ee ie ont ollin th ene gy ransm tted throughthe gu d It. i I OthB ZQ J 0 ven ien. IQ: PYL ViQ 2 n ivaadem r ve e eri ig s ems .d le i i W uide ae e s- It;-.is a.st. -iu h 0793?. f m i enii n to provide new and improved methods of controlling ,the propagation of electromagnetic .waves thr, h ieieleei icf uide it a still further .object gf 1 my invention .to

provide, new, and improved .methods. of controlling the a tenuat n e t e sm b n c e ee si .of dielectric waveguides.

lt is .a still further objectof myinvention to previd new an imp v d .mee 'j- -am l iud new e frequency module-tin el tr sne waves transmitted through a dielectric wave guide.

.B efi t te in emerg nce wi t e i l trated embodiments of my invention, 1 provide new and improved niethods [and apparatus "for ,controlling electromagnetic waves which are propagated through hollow-pipe type wave :guildes. C%enera lly speaking, -.I .p'rovide'in a holewmi typ w v uid a egi n c t ini .e are d le par cle h b .c m rfll h energy transmittedby, the electromagneti o waves through .the} guide. Stated in other words, the presence 0f. the region. of. charged electric .parti- ,cles, such as .an electron beam, serves .to control ,at will the ,eifective dielectric constant .of the .medi mw m sui e' to h-whiq th -el bl eene cmav se t nsm t e By controlling the effective dielectric constant of the medium, theIelectromagnetic Waves may ,not only bemodulated in amplitude butmay-also .h tm duleted in pha whi nek i ipb sife to c ntre the v hase ele iq 9 the e ee' rgma netie ,vtave r eived ete t u ele od me relative, to. the input. or exciting, electrode means. he b thenrepe d mensionin ,e J' h guide, that is by the choice of the longitudinal spacing of the input and output electrode means, for a particular exciting frequency and charac- -,.t. .si. e. ..e th guid t d nsity o V he r gio .959 er edelee r e iie e m be e e ,toqmo ate the frequency of the electromag- I ves received, at the, output electrode ,meansior av given, electromagnetic excitation of th suide- It .yvill be appreciated, in Viewv of p the discussion tense be nne s-th th rr nc e j tmy so .i veni n' m be inc por ted in amplitude m dulati y t m f el tr ma n t v e and mevals t app ied t seven ies st em sen ra yes eht ishes .en qu ev entitle-*- ing systems and converter or mixing circuits.

@ 7 bet e nde s andin i of .-..m intenti reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. l diagrammatically illustrates certain operating characteristics of dielectric guides of the hollow-pipe type. Figs. 2, 3 and 4 diagrammatically illustrate an embodiment of my invention wherein the region of charged electric particles constitutes an electron beam which is produced within a sealed structure associated with the guide. Fig. 5 diagrammatically illustrates another embodiment of my invention wherein the guide constitutes a sealed member or chamber and through which an electron beam is propagated longitudinally or along the axis of the guide. Fig. 6 diagrammatically illustrates an embodiment of my invention as applied to a transmitting and receiving system wherein a device built in accordance with the principles of my invention serves as a means for selectively connecting and disconnecting a receiving unit in a signalling system. Fig. '1 illustrates an embodiment of my invention as applied to a wave converting system such as an amplifier, phase or frequency converter. Fig. 8 diagrammatically illustrates an embodiment of my invention illustrated in Fig. 5 as applied to a modulating system for an amplitude, a phase, or a frequency modulating system where the modulation of the output waves is eifected in response to a controlling signal. Fig. 9 diagrammatically illustrates a modification of the embodiment of my invention shown in Fig. 2 wherein the density of the electron beam may be controlled by a suitable grid structure.

As stated above, there is a critical minimum frequency or cut-off frequency for each dielectric guide, the value of which is determined by the dielectric constant of the medium within the guide through which the electromagnetic waves are propagated and the transverse dimensions of the guide. Below this value of critical frequency, the electromagnetic waves are rapidly attenuated and the energy thereof is not transmitted an appreciable distance along the axis of the guide. Above the critical frequency. the electromagnetic waves are propagated with an attenuation and velocity determined by the propagation constant of the guide. This propagation constant it may be expressed as follows:

where a is the attenuation constant and B is the phase constant and both are real quantities whose magnitudes depend upon frequency.

If the frequency is great enough, a is very small compared to [i and waves are propagated without appreciable attenuation at a phase velocity which varies with the transverse dimensions of the guide. When the excitation frequency is below the critical frequency, the Expression 1 may still be used but now a and ,3 both become imaginary with the result that determines the attenuation and a determines the extent of wave action. Since below the critical frequency 5 is again much larger than a, the attenuation is very pronounced and the wave action is very small. Physically, this means that transmission of waves through the guide is virtually nonexistent at frequencies below the cut-ofi frequency.

Although my invention may be applied with equal facility to dielectric wave guides of various configuration, in the following discussion in order to present some fundamental considerations relative to the description of my invention, the fundamental aspects will be described with particular reference to dielectric wave guides having a rectangular cross section and wherein the height of the guide is a and the base is b.

The phase constant B may be expressed:

follows:

aiildfdtll The wave length of the electromagnetic waves propagated through the guide may be defined as:

The phase velocity Up of the Wave transmitted through the guide is defined as follows:

An inspection of the above equations, particularly Equation 3 indicates that the critical frequency is smallest for the lowest order wave and increases as either 11. or m is increased, that is as the order of the wave becomes larger. Furthermore, it will be noted that as either dimension 0. or b of the wave guide is decreased, the critical frequency increases. In addition, it should be noted that the critical frequency may also be decreased by increasing the value of the dielectric constant or by employing a material having a larger dielectric constant.

In order to simplify still further the presentation of the subject matter of my invention, it will be assumed that the dielectric is air and the system is arranged for the transmission of an H01 type wave where the electric component of the field is perpendicular to b, in which case the phase constant and critical frequency expressed by Equations 2 and 3 become:

re-err E: (real) Era (8) H (real) Hf (9) An inspection of Equations 8 and 9 indicates that for given values of at, which is the distance along the axis of the guide for excitation above the critical frequency, the magnitude of the wave varies sinusoidally with time; and furthermore,

5 int razgiven instant :the wauemas .a sinusoidal distribution along the axis. I

. Refierring :now to Fig. .the curve 411) p viren'tslthe :phase melocity, that is the speed .at awhidhua- 'long sinusoidal wave train travels ithroug h thezmedium of theidielectricfiuide. The shaded portion of the curve shown in Fig. 111 613- n esents the region of. substantially :cornplete iattienuation; ithat ismthe guide fis -opaque. :Atthe critical "frequency In, the phase velocity theoretianally- 1s infinite :and approaches the velocity of ii'gl-rt as the applied frequency approaches infinity. iherdottedportiomof the curve o representing-thephase velocity, indicates "the actual manner in which the 'p'hase velocity 'varies within ithe ueg-iomaround the critical frequency 10. 'tihe "tapering oil -oithe-curve is due Eto the losses of the:system, particularly thelosses in themetallic iconduotor' constituting thehollow pipe member.

The phase-veloo'ity is to be distinguished "from thephenomenaaacssociated with the r-ateoi transmission'of energy through the dielectric by elecitromagnetic waves. If an input signal is introduced-into a dielectric-guide, of course the cu-tput-signal will be delayed in phase in accordance with the 'time of transit of the-wave through the guide.

"Referencemay he had to Fig. '2 of the-accompanying drawings wherein i provide, in accordance with any invention, new and improved "methodsand apparatus for controlling the propagation of electromagnetic waves through a dielectric-guide which may be of rectangular cross section. Theguide may include 'a hollow-pipe type'member *having =walls of -highly-conductive material such 'as *copper or brass. The guide may"be*fabricated and includes 'a base member I ,*a topplate member 2 and an end member '3. The dielectric mediuinwithin the guide through whichthe electromagnetic waves are propagated maybe any suitable dielectricgsuch asagas, air,

or "an evacuated space.

"The guide may be excited, that-is the electromagnetic waves may'be established within the :guide "by'input electrode means such as aicon- "centri'c or coaxial transmission line including a cylinder for *tubular member '4 and a conductor 5, the latter of which "may be attached to the "top member 2. "It will be understood that other forms "of excitation may be employed, such as probes of various configurations, and -that my invention 'is not limited to the particular arrangement for excitation shown. Furthermore, it will be appreciated that the configuration of the excitation means determines, in many 'inistancesfthe type of electromagnetic waves which are es'tablished'withintheguide. The type illustrated'serves'to establish an Hui type wave.

.A suitable radiating means, such as a flared horn 15, may be employed at the transmitting end or .thegu'ide where it is desired to transmit the waves'into'iree space or into some other channel. Instead of using the horn at the end of the guide, anendwall maybe employed andsuitable probe or otherioutput electrode means maybe .used to textraidtlthe energy from the waves.

.I' provide methods and apparatus for con trolling the effective dielectric constant of the medium within the guide, thereby controlling-the attenuating and transmitting characteristics thereof. More particularly, I provide .a region .oigcharged electric particles, such as electrons, which coast with .theelectromagnetic waves in the. guide .to vcontrol the energy transmitted "thereby, or to control .amplitude, phase or fre- 6 iquency @characteristicsoitthemaves. -'Thisiregion may be coextensive with one dimensionini ithe :guide, surihras a -tcansyerseldimensiomor thesaxial :or longitudinal dimension, ;or:1the regionimay 1916 localized within a portion oinudh. dimension.

One away-finswhich ,myunvention unay ibe carried out is by providing anuelectron rheam thezwpath of which :transverse etc .ithe, direction of propagation-.ofd:he .awave through the guide.

2 II have diagrammatically illustrated an arrangement wherein. an'el'ectron. transmitted. through the guide :in. aidirection transverse to the direction of wave propagation.- The means-for producingtthe electronxbeamamay the slocatedlin azsealed 'tubular housing sorzzstrucitnre which :comprises ppantitions ssuchuascdisks 'is't-ructures and [5 which may be welded solderedito the -,disks':8;and

.The :grids l4 .and. d5 :serye several junctions, one rof whichv is .to :permit rthepassage ;of rthe zelectron,beam'therethrnugh'andranothergofiwhich rls ithe -xprovision .of, conducting "paths cacross ithe openings :it2 ;and l3. ;It will heznoted that, 35 illustratedxin-gFigs. 3 and 4 to ihe1discussed was ently, itheggrid structures :l'ilsand .zlirmay con- -stitutesystems .ioi ..;conductors :or "wires vovhichmre orthogonal, that is mutually prependicular. zvirtue .ofrthe 'arrangement; of athe :w-ires, .nonductsing paths 'areprovided :ior the. flow-rofvztranfiworse rand :longitudinal :current. incident 1.170.. the passageiof the electromagnetic waves through (guide.

litwil-lzbe appreciatedithat the disks zflaandeil :aftord a central region ,or *chamber -which vwithin the interior of the waveguide. iSuitable insulating tubular .members Ilia, :Ll and Lflrraosi tion the disks 8 and 9 and also afford spoons within which =a icathode I19 and .an-;anode s10 amay xloe-;plac.edto produce the electron beam .Catzhsode i|-9 may be-ofthe indirectly heated -t;y,pe:com- =prising .a heating elementror, filament :21, energizing conductcrs :for which extend-:ithrdll aisuitable-press .or :glass .seal 2-2 which .supported .-by a tubular conductor 23 "WhiChJSEI'NBS as :aconnection to "the cathode 121.. Thegoress :01 seal llmay be connected to the conductor #23 .by means .of al-flanged-metallic tubing {'24.

The electron v lceam density may, of :course, :be controlled by-yar-ying the -.voltage.-applied between the anode 2c and the cathode 49. .It will rbe ap (preciated :that .the electron .beam ,density may-be v.variedinresponse to any predeterminedcontroiling signal, thereby controlling the efieotivedielectric constant of the medium within the guide 2&1 will. ,Diagrammatically, iior thepurposes rof illustrating one way. in which the electron.JJeam density :may be varied, ,-I hayea-shownta. battery,;B and .an adjusting 'means for controlling :the potential difference between .anodezand cathode.

7 A switch C, of course, may be connected in this circuit.

Fig. 3 shows in prespective the portion of the structure 1 including the disks 8 and 9 and an insulating cylinder 17 which positions the disks. Grids I4 and I are also shown to cover the rectangular openings I2 and I3.

In Fig. 4 a perspective view is illustrated of apparatus built in accordance with one embodiment of my invention, such as Fig. 2, and shows the manner in which the anode l9 and the oathode 20 are positioned relative to the rectangular openings.

In explaining one method of operating the embodiment of my invention illustrated in Fig. 2, it will be assumed that the guide is excited at a frequency slightly above the critical frequency of the guide under those conditions where the electron beam density is zero. In this case, the electromagnetic waves will be propagated through the guide and the phase constant, the velocity of propagation, and the wave length of the transmitted wave will, of course, be determined by the equations discussed hereinbeiore. Upon the transmission of the electron beam between the anode 2i} and the cathode 19, the dielectric constant of the medium within the guide, which for the purposes or" explanation will be assumed as being air, will be decreased to a value less than 1, consequently resulting in an effective dielectric constant which is less than unity and thereby raising the effective critical frequency of the guide. As a result, the electromagnetic waves will be highly attenuated and energy will be transmitted only a very small distance along the guide from the input electrode means. Upon interruption of the electron beam, the effective dielectric constant becomes equal to that of air and the waves are propagated through the guide. Therefore, one application of my invention may be represented as rapidly changing a dielectric wave guide system from an attenuator to a wave passer or propagator.

It is to be understood that in accordance with the teachings of my invention, the wave guide system may be designed so that transition from an attenuator or a propagator, or vice versa, may be accomplished by changing the density of the electron beam from one of higher intensity to one of lower intensity, or vice versa, and that it is not necessary forthe utilization of my invention to interrupt completely the electron beam.

The manner in which the electron beam affects the dielectric constant of the medium through which the waves are propagated may be viewed from the standpoint of the interaction of the transmitted waves and the waves produced by the electron beam. For a more theoretical explanation of the manner in which the transmitted waves and the waves of the electron beam interact to modify the efiective dielectric component of the medium, reference may be had to my paper entitled Space charge and field waves in an electron beam, published in the l ugust 1, 1939, issue, vol. 56, of Physical Review.

Generally speaking, it may be said that the effective dielectric constant of the medium is a function of the difference of the dielectric constant of the medium with no electron beam present and a quantity which is directly proportional to the number of charged particles per unit volume, the square of the unit charge of each particle, and inversely proportional to the mass of each charge and some function of the frequency,

and if a magnetic field is present, some function of the magnetic field.

It will, therefore, be appreciated that as the charge density of the electron beam increases, the effective dielectric constant decreases, being at all times less than 1 due to the presence of the beam.

Refering again to Fig. 1, it will therefore be appreciated that by control of the density of the electron beam the operation of the wave guide system shown in Figs. 2 and 4 may be selectively controlled to efiect transitions from the attenuation region to the transmitting region. As the intensity of the electron beam is increased, the effective dielectric decreases to a value which prevents the propagation of waves through the guide. That is, for increased values of an electron beam intensity, the phase velocity Up becomes greater, at all times being greater than the velocity of light, and approaches infinity at the cut-off frequency; the cut-01f frequency, of course, being a function of the effective dielectric constant. Moving in the other direction along curve u it will be appreciated that as electron beam density is decreased, the effective dielectric constant of the medium is increased to that value which will permit propagation of electromagnetic waves for the particular value of frequency and the dimensions of the guide.

The embodiments of my invention illustrated in Figs. 2 and i may be operated as an amplitude modulator, that is may be operated to control the magnitude of the electromagnetic waves transmitted by the guide. For example, the system may be made to operate along a vertical portion q--r of the attenuation curve or shown in Fig. 1. By controlling the electron beam intensity, the attentuation within this region is materially varied, causing an appreciable variation in the amplitude of the transmitted waves. Consequently, the waves transmitted through the guide, or the waves received at electrode receiving means, are controlled in magnitude in response to the beam density.

In Fig. 5 I have diagrammatically illustrated another embodiment of my invention as applied to a dielectric wave guide which may be employed as a phase modulator or a frequency modulator. In the arrangement of Fig. 5, the wave guide may also be of rectangular cross section of dimensions similar to that shown in Figs. 2 and 4 and in which the entire guide through which waves are propagated is hermetically sealed so that the electron beam may be transmitted longitudinally through the evacuated guide, the end wall or plate 25 serving as an anode and the end wall or plate 25 being provided with a rectangular opening including a grid 2? through which the electron beam passes. A cathode 28 of the indirectly heated type may be employed, positioned as illustrated relative to the guide and the grid 2?, as a source of electrons. Cathode heating current is supplied to the fila- Inent 29 through conductors 3i? and 3: and a conductor 32 is connected to the cathode and serves as a cathode lead. Conductors 3532 may be supported by a glass press 33 and terminate in a plug of the type indicated as a ready means for establishing a cathode heating circuit and oath,- ode connection.

A tapered metallic end enclosure 313 which is sealed may be empioyed to connect the metallic walsl of the guide to the glass press assembly 33. This member may be sealed to the walls of the press by a suitable glass to metal seal, such as nickel, iron and cobalt alloy. I provide input apes-e51 9? electrode means: which; may; take the: form. ot a concentric or coaxial transmission line: comprising-a tubular member 3.5;and1a coaxial. conductor 35,,the. former" being connected-tothe top of the wave,- guide: and: the: latter being conductively connected to the-bottomot the guide. A seal 3:1 may be positioned as; indicated to: maintain. anevacuated space:within-thaguide- Inasmuch as the electromagnetic. waves are transmitted, longitudinally through, the; guide at aid'efinite; frequencyand have a wave length. Ag as: indicated above, where itis desired to phase modulate the waves relative lac-input signals, I provide output electrode; means which may comprise a concentric. or coaxial. transmission .linezincluding-v a. tubular conductor 38- and a condiictor 39,.theformer oi..which. beconnected tothe. topof; the guide and the latter of which is: conductivelyconnected tothe bottom. Of course, suitable sealing means is. also provided for this. line. The distance Lbetween thecenters oiythewinput and; output. electrode, means determines. (in con jnnction 'withthe. wave. length of transmitted wave, the transverse. dimensions eitheguide and theelectronbeam. density). the angle of.-displacement -01: lag. between. the input signal and the outputsignals.

Consequentlh. itis. to. be. understood, that I providemeanswhereby an.electromagnetic wave maybe phasev modulatedwith respect to the in.- .putron' excitation. wave controlling. the. electronheaml density. In. general terms,v the. beam density QOIItXZOISvxthB phase constant, and. consequently. controls the phase. velocity and. wave lengthv of, the transmitted. wave, By varying the density of the beam, the. angle of displacement between. input. and output electrode means isaccordingly controllable, Qne wayin which the. embodiment of my invention. illustrated; in- 5 may be. Operated is to design thesystem,,.that is the transverse dimensions t the.-,guide,.'the lengthL,v and the exciting. frequency for a given value of" electron beam. density so that for a particular condition of operation thephase displacement between the input; andoutputwaves is zero. By decreasing the. density of the electron beam, theelfective dielectric cOnstantNis consequently increased and the wave length X of the transmitted wave; is consequently decreased; producing a phase displacement which i's'a function of thebeam den"- sity: Flor-"example; when the electron. beam density is maximum, the 'system may' be arranged sothatthephase' displacement is practicallyzero, anijfor zerobeam density-the phase displacementmay'becloseto E'X-Zbr radians A When-the d'evioes built irr accordance with my invention; such as thatsh-ownih-Fig. arev employed as phase or frequency modulators, the

system" may be operated within that region g'h trot the transit time of the wave; through the guide since a variation in the electrode beam parameters is a means of changing. the phaseor. time delay betweenmthe input and output electrode means. To obtain appreciable. phase modulation in this manner, itisappreciated that thesfield of application is toextremely high frequency waves. However, systems built in ac:- cordance with my inventionma-ybe applied to arrangements: where; it: is.- desired. to obtain fre--- quency modulation of an electromagnetic wave. For: example, the distance L, may be made 1: meter 'long. If the electron beam. density is made: tovary between two extreme valueswhich correspond to-a large phase velocity comparedwith that of light and. approximate light velocity, then: something of the order of; 21r radians phase shift may be obtained. for a 1 centimeter wave. Such: frequency modulation is sufiicient for a. wide band frequency modulation communicationzsystem When it, isdesired to focus, the electronbeam, I mayemploysuitable-apparatus such as axfocusing magnetic coil 40. having its principal; axis preferably in coincidence: with thelongitudinal axis of the guide. The resultant. characteristics of any electron beam and; an electromagnetic wave when the; beamis-s focused; in: this-manner is treated to some extent: in; my above? identified paper.

Fig; 6 diagrammatically illustrates; anaembod'i ment of my' invention-as: applied to:-a:re.ceiving= transmitting system. wherein a. high frequency transmitter 4;]: is. connected: to. a radiative: and reception element,. such as-arr antenna; 42, and wherein a receiver 43; is employed; In some. direction systems, such as thOSBillSEd for thelocation of. distant objects; it. is desired: to prevent reception by the receiver.- of the: high intensity electromagnetic waves;- emanating from a. near.- bytransmitter due; tothe faict that. theintensity of? the transmitted waves is:suilicientli great in some instances. to damagetithc receiver. Iicon nect between-the transmitter-and the receiver I one of the devices built in accordance with my invention; such as the-arrangements: shown. in Fig. 2' and Fig. 5,, sovthatthe receiveris. protected while thetransmitter is operating. The device when, used as a protective: or control-element is shown' diagrammatically as"4;4- ine; Fig. 6-. When device 44 is employed in this n'ranner,v it is. to be understoodythati in. place of the flared horn 'of-"Fig; '2; the receiver may be; connected: by means of an: output electrode means such as that shown in Fig. 5.

I also provide means, for selectively controlling the: operation of the device 44 and the transmitter 41-: Referring: to Fig. 6;, I. have there shown diagrammatically-a. simple arrangement comprising a key 45' provided": with; contacts .46 and-.41, the former-of'which are closed; to establish-:an electronbeam in: the device" 44, thereby protecting the receiver when the transmitter is in operation. The contacts; :41- are-connected to render, the transmitter operative by depression of the key, The key 45 may be arrangedsozthat contacts 46- and 41 are closed simultaneously, orvcontacts: 46 are closed before contacts. 4?, so that the electron beam is: always present within the device 44 atithe time" the transmitter is intensity of the outgoing electromagnetic waves and the received electromagnetic waves. For example, I may employ a protective device which establishes the electron beam when the intensity of the electromagnetic waves of the system or antenna is above a predetermined value as, for example, when the transmitter is operating, thereby protecting the receiver.

When the transmitter is operating, the electron beam is established within the device 44 causing it to operate as an attenuator. When it is desired to receive the reflected waves caused by distant objects, the transmitter of course is not operated and the device 4 1 permits the reception of signals by the receiver 43. This is, of course, effected by decreasing the electron beam density or interrupting the beam completely so that the device 44 operates as a prop agator of electromagnetic waves.

In Fig. 7 there is diagrammatically illustrated another application of my invention and which includes a device generally similar to that shown in Figs. 2 and 4 but modified by the employment of output electrode means, such as a concentric or coaxial transmission line including a tubular member 4% and a conductor 49. Other elements of the device have been assigned reference numerals corresponding to those of Fig. 2. In this arrangement of my invention, the input electrode means may be connected to an ultra high frequency generator or an antenna, and the output electrode means may be connected to a receiving device. The control of the electron beam may be effected in response to a signal, produced by a device 5%, which is amplified by a suitable electronic amplifier 51. It is to be understood that the control means for the electron means may be connected directly to the input electrode means comprising the tubular member 4 and the conductor 5, in which case for an arrangement similar to Fig. 6 the electron beam will be established if the intensity of the electromagnetic waves in the antenna 42 circuit exceeds a predetermined value.

The arrangement shown in Fig. '7 may also be operated as an amplifier for the signals produced by the device 50, in which case the magnitude of the waves received at the output electrode means may be controlled by the intensity of the electron beam.

Fig. 8 is another diagrammatic illustration of one way in which the device shown in Fig. 5 may be applied to a modulating system, such as a magnitude, phase or frequency modulation systern. In this arrangement, the voltage impressed acrcss the anode and cathode, which produces the electron beam, is varied in response to a signal source or in response to a received signal by means of a device 52. If required or desired, an electronic amplifier 53 may be interposed between the signal source and the wave guide.

In the embodiments of my invention described heretofore, the electron beam density has been controlled by variation of the anode-cathode voltage. In Fig. 9 I have diagrammatically illustrated a modification of the arrangement shown in 2 wherein the electron beam density may be controlled by means of a grid structure, such as a grid 5 which may be positioned intermediate the cathode H3 and. the grid mesh 44. The grid it: may be insulated from the plates I and 2 of the wave guide by means of a ring of insulation 55 so that the potential of grid 54 may be maintained negative relative to that of the cathode l9. Grid may be supported and attached to a metallic disk 56 positioned between the insulating tubes l8 and H, and may be connected to an external circuit through a suitable high frequency structure or transmission line if it is desired to vary the'potential thereof at high frequency.

It will be apparent that the various circuit arrangements for controlling the intensity of the beam and for effecting control of the transmitted waves in the manner explained heretofore may also be applied with equal facility to'the arrangement of Fig. 9 wherein the potential of grid 54 serves to effect the desired control.

The electrostatic control member or grid 5t may also be positioned between grids M and 35, that is may be positioned to lie within the portion of the electron beam within the wave guide.

In a similar manner, it will also be appreciated that the embodiment of my invention shown in Fig. 5 may also be provided with an additional grid structure for controlling the intensity of the electron beam. Such a grid structure may be placed between the cathode 2B and the grid 21, or may be positioned within the guide at any optimum point along the beam.

While I have shown and described my invention as applied to particular systems embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United, States is:

1. In combination, a dielectric wave guide comprising an elongated hollow member, cathode means external to said member for producing within the space enclosed by said hollow member an electron stream having a component parallel to the longitudinal axis of said member and occupying substantially the entire wave guiding region therein, means coupled to said member for exciting said member at a frequency somewhat greater than the cut-off frequency established by thev dimensions of said member and the dielectric constant of the medium within said member, output means spaced longitudinally from said last mentioned means by a distance which is relatively great with respect to the wave length corresponding to the frequency of excitation of said member, and means for, controlling the charge density of said stream to phase modulate the electromagnetic waves received at said output means.

2. In combination, a' dielectric wave guide comprising an elongated evacuated hollow member for transmitting electromagnetic waves dielectrically and comprising at one end thereof a cathode and at the other end thereof an anode for producing an electron beam along'the longitudinal axis of said guide, means connected to said guide for establishing electromagnetic waves therein, and output electrode means spaced longitudinally from said last mentioned means.

3. In combination, an elongated evacuated dielectric wave guide having at one end thereof a metallic wall which serves as an anode and at the other end thereof a wall provided with an opening, a grid lying across said opening to provide a path for the flow of current incident to the waves in said guide, an evacuated member asssgacr positioned toenclose the endof said guide providing said opening and having therein a cathode, the electrons emitted. thereby passing through the grid to the end plate constituting said anode, inputelectrode means for establishing electromagnetic waves within" said guide, and output electrode means spaced longitudinally from said input electrode means,

4. In combination, .a dielectric wave guide comprising an elongated hollow member, means for producing. an electron beam within the space enclosed by said hollow" member, means coupled to said member'fo'r exciting said'. member at a frequency somewhat greater than the cut-on frequency established/by the dimensions of said member and the dielectric constant of the medium within said member, electromagneticmeans for focusing said beam along a path substantially coextensive with the region of effective wave propagation within said member, output means spaced longitudinally from said exciting means by a distance which is relatively great with respect to the wave length corresponding to the said frequency of excitation of said member, and means for controlling the charge density of said beam to phase modulate the electromagnetic waves received at said output means.

5. In combination, a dielectric wave guide of the hollow-pipe type comprising an evacuated structure including means for producing an electron beam along the longitudinal axis of said guide, means for establishing in said guide electromagnetic waves of high frequency, output electrode means displaced longitudinally of said guide from said last means, and means for controlling the intensity of said beam to control the energy of said waves at the output electrode means.

6. In combination, a dielectric wave guide of the hollow-pipe type comprising a metallic member through which electromagnetic waves may be propagated, means for establishing electromagnetic waves in said member, an evacuated structure supported by said guide and extending therethrough in a direction perpendicular to the direction of propagation of the electromagnetic waves through said guide, electric discharge means within said structure for producing an electron beam, and means for controlling the intensity of said beam to control the amount of energy transmitted by said waves.

'7. Incombination, a dielectric wave guide for propagating electromagnetic waves and comprising a metallic member of rectangular cross section, a cylindrical structure extending through said member transverse to the direction of propagation of said waves and comprising a nonresonant central portion bounded by a pair of perforate coaxial metallic disks positioned contiguous to the top and the bottom of said guide to afford a substantially continuous conducting surface, and means within said structure and displaced from the central portion for producing an electron beam. v

8. In combination, a dielectric wave guide for propagating electromagnetic waves and comprising a metallic member of rectangular cross section, a cylindrical structure extending through said member transverse to the direction of propagation of said waves and comprising a central portion bounded by a pair of coaxial metallic disks contiguous to the top and bottom of said guide to afford a substantially continuous conducting surface, said disks being providedwith rectangular openings the principal dimension of which is substantially equal-to a transverseidi mension of said guide, a pair of conducting grids. attached tosaid disks and substantially covering saidopenings to provide transverse and longitudinal paths for the conduction of'currentincident to the transmission of electromagnetic waves through said guide, means 'positioned w-ith;-- insaid structurecomprising an anode and a: cathode for producing an electronbeam which passes through said openings, and an electrostaticgrid control means for controlling the electron beam density.

9 Incomoination, adielectric wave guide of the: hollow-pipe type comprising a metallic memher through which electromagnetic wavesmay be propagated, means for establishing electro-- magnetic waves within said guide, a tubular structure extending through said member sub stantially perpendicular to the direction of wave propagation through said guide and comprising a central chamber including metallic partitions positioned relative to said member to afford substantially continuous conductive paths, said partitions being provided with openings, grid members lying across said openings and attached to said partitions and serving as longitudinal and transverse conducting paths for the flow of electric current incident to the transmission of the electromagnetic waves through said guide, means within said structure for producing an electron beam, and second grid means for controlling the intensity of said beam.

10. In combination, a dielectric wave guide of the hollow-pipe type comprising a metallic member through which electromagnetic waves may be propagated, means for establishing electromagnetic waves within said guide, 'a tubular structure extending through said member substantially perpendicular to the direction of wave propagation through said guide and comprising a central chamber determined by metallic partititons positioned relative to said member to aiford a substantially continuous conductive path, said partitions being provided with openings, grid members substantially covering said openings and attached to said partitions and each serving as longitudinal and transverse conducting paths for the flow of current incident to the transmission of the electromagnetic waves through said guide, and means within said structure for producing an electron beam.

11. In combination, a guide for transmitting electromagnetic waves dielectrically including a hollow-pipe type member, means for establishing electromagnetic waves in said member at a frequency close to but above cutoff, discharge-pervious means forming an electrically continuous part of the wall structure of said member, means for producing an electronic discharge extending through said disoharge-pervious means and within said member in a region traversed by said waves and means for controlling said electronic discharge to vary the propagation of said waves. 12. In combination, a guide for transmitting electromagnetic waves dielectrically including a hollow-pipe member, means for propagating electromagnetic waves longitudinally within said member at a frequency close to but above cutoff, means for producing a stream of charged particles within said member in a direction parallel to the direction of wave propagation and in a region substantially coextensive with the propagating path, and means for producing controlled variations in the density of said waves from point to point along said propagating path thereby to produce phase modulation of said electromagnetic waves.

13. In combination, a dielectric wave guide comprising an elongated hollow member, means for producing within the space enclosed by said member an electron stream parallel to the longitudinal axis of said member and extending along the wave-guiding portion thereof, means coupled to said member for producing wave propagation longitudinally therein at a frequency 0 close to but above cutoff, output means Within said member and spaced longitudinally from said last-named means by a distance which is relatively great with respect to the wave length of said electromagnetic waves, and means for producing controlled variations in the density of said electron stream from point to point along its axis to phase modulate the electromagnetic waves received at said output means.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date Girardeau Aug. 20, 1912 Southworth Feb. 1, 1938 Southworth Apr. 11, 1939 Van Mierlo Nov. 26, 1940 Chaffee Mar. 18, 1941 Blewett et a1. May 13, 1941 Bowen Aug. 26, 1941 Hahn Mar. 10, 1942 Barrow Apr. 13, 1943 Llewellyn Jan. 23, 1945 FOREIGN PATENTS Country Date Australia Oct. 22. 1941 

